The present invention relates to a semiconductor laser with constant differential quantum efficiency or constant optical power output.
The differential quantum efficiency .eta..sub.ext and the optical power output P.sub.opt of a laser diode are strongly temperature-dependent. For many applications, however, either a nearly temperature-independent differential quantum efficiency .eta..sub.ext or a nearly temperature-independent power output P.sub.opt are desirable. In optical communication systems using intensity modulation, only a temperature-independent differential quantum efficiency makes it possible to convert a constant frequency swing of the control current into a constant modulation depth of the optical signal. If a laser diode is used as a transmitter which must have a constant light output, the output should be temperature-independent (at a constant injection current).
DE-OS No. 35 34 744 discloses a laser device with stabilized power output in which the current flowing through the laser diode is influenced by a temperature-dependent compensating resistor in such a way that the optical power emitted by the laser diode is largely independent of temperature. To accomplish this, it must be ensured that the temperature-dependent resistor and the laser diode have the same temperature.
The prior art device has the disadvantage that even small temperature differences between the laser diode and the compensating resistor result in large outputpower variations, which is not sufficient for many applications.